Thousands of households are paying around £100 a year more for gas and electricity than others on the same tariff just because of where they live.

The energy companies claim this is because it costs more to supply energy to certain addresses.

But the higher bills are also due to a legacy of privatisation that has seen providers offer cheaper deals to new customers to win their business.

Money to burn: Energy bills are £100 more in St Ives than Skegness

Despite repeated campaigns by regulator Ofgem and consumer bodies to get customers to switch, many largely older, loyal households have stuck with their original company — and are paying much more than they need to as a result.

All of the Big Six energy suppliers — British Gas, EDF Energy, E.ON, Npower, Scottish and Southern Energy and Scottish Power — operate a postcode lottery that sees customers paying different prices for the same deal depending on their address.

For example, according to Money Mail research last month, the average customer in North Wales on Scottish Power’s Online Fixed Price Energy July 2015 tariff pays £1,137 a year for gas and electricity.

But a similar customer in the East Midlands pays only £1,029 — £108 less — for precisely the same deal.

British Gas’s Fixed Price May 2015 deal is also cheaper for customers in towns such as Leicester or nearby Skegness. They pay just £1,129 a year compared with households in St Ives in Cornwall or towns in Devon, which fork out £1,226 — £97 more.

But when it comes to which areas pay the most or least, there is no clear pattern.

Dual-fuel customers in Yorkshire on Scottish and Southern Energy’s One-Year Fixed-Price tariff get a better deal than those in the South-West. The Yorkshire homes pay just £1,088 a year, while the South-West households cough up £1,169 (£81 more).

Yet if the same Yorkshire customers were on British Gas’s Fixed Price May 2015 tariff, they would be paying £24 more than those in the South-West.

Suppliers claim the reason they charge customers around the country different prices is largely down to transportation costs — it is more expensive to supply homes in some parts of the UK than in others.

Mark Todd, director of the price comparison website Energysavinghelpline, says: ‘Gas is typically cheaper in the East of the country, as that is the direction from which it comes in.

‘Much comes from Russia and Europe, and it costs more to pump it hundreds of extra miles to the West of Britain.

‘And if you live in an area well served by power stations, you may find electricity is cheaper than if you live further out. But the pattern is not consistent and the differences can vary hugely.’

Another major reason prices differ across the country goes back to the way the energy industry was privatised in the late Eighties and early Nineties.

Differences: The cost of energy varies around the country as it costs different amounts to supply energy to certain addresses

Until then, gas and electricity firms had been owned by the government — the company we now know as British Gas used to supply all homes in the UK with gas, while there were 14 local electricity suppliers that served homes in their area. These included Swalec in the South-West, London Electricity in the capital and Midlands Electricity for the Birmingham area.

But after privatisation, these were gradually taken over by what we now know as the Big Six.

Now households can switch to any supplier. However, a large number of people have stuck with their original regional provider.

As a result, many suppliers still dominate the region they first served — for example, EDF (which incorporated London Electricity and other southern firms) is popular in London and the South, and Npower (which bought Midlands Electricity and Yorkshire Electricity) is big in the Midlands and Yorkshire. Research by the Energysaving helpline shows that electricity suppliers are almost always more expensive in areas where they have the most customers, while British Gas is the most expensive provider of the Big Six in 13 out of 14 regions.

Households that have never switched supplier are paying up to £400 a year more than those who have switched to the best deals, according to price comparison website Moneysupermarket.

Yet nearly two-thirds of households have never bothered to switch, according to energy regulator Ofgem.

Mark Todd says: ‘It clearly does not pay to stay on defaults. This is why switching generally saves money, particularly with gas. Having dual fuel generally gives discounts that save more. Then fixing and looking at small suppliers often saves the most.’

A spokesman for Energy UK, the industry body which represents the power companies, says: ‘Network charges make up around 20 per cent of the bill and are agreed between the separate network companies and the regulator, Ofgem.

‘They will vary in different parts of the country, depending on the amount of work needed to upgrade and alter wires or pipes.

‘Switching can save people money. Around a quarter of a million people switch each month, with 289,000 doing so in April alone.’

IS IT TIME TO SWITCH? HOW TO DO IT YOURSELF

Energy tariff prices are in a constant merry-go-round with suppliers battling to pinch customers - you - from each other.

Shrewd consumers can take advantage of this by doing exactly that - moving deals every six months to a year to ensure they are on THE cheapest deal. Even moving every other year will save you significant amounts.

Suppliers offer their cheapest rates via online tariffs so if you're ready to switch, it will certainly pay to do so.

If you are one of the millions of people who have NEVER switched (i.e. stuck with your original supplier), then you will DEFINITELY save a big chunk of cash, possibly as much as £300 a year.

Prices are different all over the country and the cheapest supplier for you will depend where you live. You only need to be interested in the tariff that is going to be cheapest where you live, so do your own comparison to find the best price.

For full details of how to switch your provider and where to find the best deals check out This is Money's guide